Combined diode detector and amplifier circuit



`Fune 23, 1936. .D Q BURNslDE COMBINED DIODE DETECTOR AND AMPLIFIERCIRCUIT Filed Sept. 27, 1933 NTN,

Patented June 23, 1936 UNITED STATES COMBINED DIODE DETECTOR lANDAMPLIFIER CIRCUIT Don G. Burnside, East Orange, N. J., assignor to RadioCorporation of America, a corporation of Delaware Application September27, 1932, Serial No. 691,115

9 Claims.

My present invention relates to radio receivers, and more particularlyto receivers utilizing tubes adapted to simultaneously perform diodedetection, audio amplification and automatic volume control functions.

There has been disclosed by T. M. Shrader, in application Serial No.622,140, filed July 12th,

1932, radio receiver circuits employing multifunction tubes adapted toperform diode detection, audio amplification and automatic volumecontrol. Such tubes are designated as 55 tubes, and utilize independentdiode detector and amplifier sections. The essential feature of the tubevconstruction involves, the disposition of the diode anode, `or anodes,adjacent a portion of the cathode, this portion supplying electronssolely to the diode anode. It will, therefore, be seen that the fullcathode surface in the 55 tube is not utilized to feed electrons to theamplifier section.

Accordingly, it may be stated that it is one of the important objects ofthis invention to provide a signal receiving system wherein amultifunction tube is employed for simultaneous diode n detection, audioamplification and automatic volume control, the tube being especiallycharacterized by the inclusion within the tube envelope of a diode anodewhich employs the electron stream supplied to the amplifier section ofthe tube, the said diode anode nevertheless `drawing `only a portion ofthe electron stream.

The aforementioned 55 tube has revealed an undesirable characteristic inactual operation. When such a tube is employed in a multi-funcn tionnetwork of the type disclosed inthe aforesaid Shrader application, it isfound that -an appreciable bias voltage is developed across theYoliodeload when no signal is applied 'tothediode The development ofthis bias voltage is ydue -to the effect of contact potential and/orinitial electron velocities. y

Accordingly, it is pointedout that fit is another important object ofthe present invention to secure :simultaneous vdiode detection, audioamplification and automatic volume control in 'a network employinga-single tube, the diode section of fthe tube-being so ...constructedthat the effect of contact potential and/or initial electron velocitiesis much less than when using a 55 tube, resulting in but little, or nobias voltage beingfdeveloped across the diode fload when lno signal isapplied to the network.

Still another'important objectof this invention is to provide in areceiver `a tube which utilizesa filament heating current of 2 volts,and that can be efficiently-used as va combined detector, :audioamplifierA and `automatic volume kcontrol tube.

`Andrstill-anotherobject of this invention is'to provide-.acombineddiode detection, audio amplication and automatic volume controlnetwork Whichutilizes a tube of the type having .a cathode, Aan lanode,and five interposed grid electrodes, the gridsecond `from the cathodedrawing only a portion of the v.electron vstream `and functioning `as adiode detector anode.

.Still other kobjects of `the invention are to improve generally-thesimplicity and Aefliciency yof receivers employing multi-function tubes,and yto particularly provide a receiver Vof this type which is not onlyreliable in operation, but economical- ,ly manufactured and assembled.

The novel features which I .believe to -be characteristic `of `myinvention are set forth in par.- ticularity in ,the appended claims, theinvention itself, however, as .to both its organization and method ofoperation will best be understood .by reference to the followingdescription taken .in connection with the .drawing in which I -haveindicated diagrammatically several circuitQorganizations wherebymyinvention may be vcarried Vinto effect.

YIn the .drawingzl Figure 1 diagrammatically shows a radiore- .ceiver ofthe superheterodyne type embodying `the ,present invention.

Figure 2 shows a modified `form of the multifunction network.

`Referring now to the Yaccompanying drawing, .wherein vlike referencecharacters -in theY two figures represent Vsimilar circuit elements,there-is ,shown in Figure 1 aconventional type of superv`heterodynereceiver. The source of signals, which Vis -conventionally represented,may be the usual grounded antenna circuit, the signal ycol- -lectordevice-of an `automobile receiver, v0r any .other `desired. Vsignalcollection means. The signal .collector is shown feeding the collectedsignals, which signals preferably are .in u.the vbroadcast frequencyrange, to a `combined detectoroscillator network. This network,represented bythe numeral l, is not shownvinits structural `details forthe reason that those skilled in the art are `well acquaintedwithsuchdetails.

As a fspecific example of the combined `detector-oscillator network,reference is made to ,the arrangement shown yin Haines applicationSerial N0..663,171, filed March'ZBth, 1933. rThe arrangement shown` inthis Haines r.application employs a tube known V'as a 2A7 tube. The tubeisfalso known asa pentagrid converter, and Vcons1sts,.in additionto thecathode and plate, of five grids disposed between Vthe cathode andplate. Of-coursa'anybther well known type of detector-oscillator networkmay be A employed 1in the network I.

Theintermediate frequency output of the -network I is fed-to theintermediate frequency amplier network v2, and the amplifiedintermediate frequency energy :is then transmitted vthrough the tunedcoupling M1 to the multi-function tube 3. The latter is of the typeknown as 1A6, and includes a filament 4 that operates with 2 volts and acurrent of 0.06 ampere. The tube also includes an anode 5', and fivegrids between the filament 4 and the anode 5. The actual construction oftube 3 may follow the construction shown for the 2A7 tube in theaforementioned Haines application. Briefly, in such a tube the grids areinterposed between the cathode and plate so as to be passed insuccession by the electron stream from the cathode to the plate, and arepreferably arranged coaxially with the cathode. The grids are the usualwound grids, each consisting of two parallel grid rods and a helix ofcylindrical grid wire with its turns fastened to the grid rods. The gridimmediately adjacent the filament 4 is designated by the numeral 5. Thenext grid, designated by the numeral 6, is the diode anode, and isconstructed to draw only a fraction 0f the electron stream. Theelectrode 6 preferably has no grid wire helix, but is merely two gridrods mounted in alignment with the grid rods of the remaining grids. Theconventional representation of the electrode 6 is to be understood ascovering the aforementioned construction, or any other constructionwherein the diode anode 6 is made to draw only a portion of the electronstream, while being in the path of the electron stream from the filament4 to the remaining grids and the anode 5. The grid 'I and the grid 8 areelectrically connected together, and between them is disposed the grid9, which functions as the audio signal grid. The diode detector circuitincludes the electrode 6, the signal input circuit I0, the resistor R1,the latter being shunted by the radio frequency by-pass condenser II,and the connection to the electrical center of the filament resistor Rz.The audio frequency signal potential developed across resistor R1 is fedto the audio grid 9 through a path which includes the condenser I2 andthe lead I3, it being noted that one side of the condenser I 2 isconnected to the negative side of resistor R1. The audio grid 9 ismaintained at a vnormal negative bias potential through a path whichincludes the biasing source I4 and the resistor I5, and the lead I3, thesource I4 having a potential value of about minus 3 volts. The directcurrent potential developed across resistor R1 is utilized for automaticvolume control of the preceding networks, and the path designated AVC isto be understood as representing the automatic volume controlarrangement which functions to reduce the gain of the amplifier 2 andthe detector-oscillator I with increasing signal carrier amplitude. Theresistor I6 and grounded condenser I1 provide the usual radio frequencyfilter circuit employed inthe automatic volume control path, the diodedetector side of the lead I8 being connected to the negative side ofresistor R1.

The audio amplifier section of tube 3 includes, in addition to the grid9, the grids 1 and 8, as Well as the anode 5'. The grids 'I and 8 areconnected by a lead I9 to the positive side of a potential source 20,the potential difference between the grids I and 8 and the filament 4preferably being plus 30 volts. The anode 5 is connected through thepositive side of the potential source ZI to a path which includes thechoke 22, the resistor 23 and the lead 24. Of course, the sources 20 andZI can be a common potential source, and

in such a case the potential difference between the anode 5" and thefilament 4 is preferably plus volts. The amplified audio frequencysignal energy is fed to a succeeding audio frequency load network, andthe latter may comprise further audio amplification networks and/ or areproducer.

The grid 5 is connected to the filament electrical center through a lead25. Appropriate by-pass condensers are connected between the grid 5 andthe circuit including anode 5', and also between the grid 5 and the leadI9 to the positive grids '1, 8. It is believed that the operation of thearrangement shown in Figure l will be clearly understood from theaforegoing description, as well as by Virtue of the followingexplanation.

Heretofore there has not been available a 2 volt tube that could be usedas a combined detector, amplifier and automatic volume control tube.

The 55 type of tube additionally possesses the undesirable feature ofdeveloping bias voltage across the diode load when no signals areimpressed on the diode. It has been found, however, that the tube 3functions in a satisfactory manner when a 2 volt filament heating sourceis only available. Since the grid t has but little effect on theelectron stream because of its design, it is used as the diode detectoranode. It is particularly useful this way when the grid 5 is tied to thefilament 4. explanation of the operation involved, it is pointed outthat the maintenance of the grid 5 at cathode potential results in asubstantial suppression of the effect of contact potential and/orinitial electron velocities upon the diode anode 6. At the c no-signalcondition little or no bias voltage is def veloped across the dioderesistor R1, thus avoid-- ing a reduction in the sensitivity of thecontrolled amplifiers through the AVC lead. It will, therefore, be seenthat the tube 3 embodies a diode section which includes the lament 4,the suppression grid 5 and the diode anode grid 6, as well as a tetrodeaudio amplifier section which includes the filament 4, the audio signalgrid 9, the grids 1, 8 functioning as a positive screen grid, and theplate 5. The tube not only operates efficiently from a 2 volt heatingsource in the manner specied, but possesses the additional advantages ofpermitting the entire cathode surface of the cathode 4 to supplyelectrons to the tetrode electrodes,

and substantially preventing the occurrence of bias voltage across thediode load when no signals are impressed on the diode.

In Figure 2 there is shown a modified method of using the tube 3 in thereceiver network. Here the i screen grid section of the tube operates asan intermediate frequency amplifier to supply carrier Voltage to thediode anode grid 6 through the medium of the tuned transformer 30. Inother words, the tuned input circuit I0, which is tuned to theintermediate frequency, feeds intermediate frequency energy to thetetrode amplifier which comprises the filament 4, the signal grid 9, thescreen grids 1, 8 and the plate 5. The amplified intermediate frequencyenergy is transmitted to the tuned secondary circuit 3| of thetransformer 30, and the diode comprising filament 4, suppressor grid 5and the diode anode grid 6 recties the intermediate frequency energy.The audio frequency component of the rectified energy which is producedacross resistor R1 is fed to the succeeding audio frequency network,while the direct current component is employed for automatic volumecontrol.

It is pointed out that the first grid 5 may be employed as the diodeanode in place of the electrode 6, the grids 1 and 8 functioning toelectrostatically shield the audio grid from the carrier on the grid 5.Used in this manner the recti- Without going into any theoretical lilcation efficiency of the diode is relatively higher. 75

However, such use may be found objectionable in that with a modulatedcarrier on grid 5 a modulated electron stream is supplied to the tetrodesection of the tube. The action of the grid 5 on the electron stream mayresult in undesirable detection in the tetrode section. It is for thisreason that the grid 6 is preferably employed as the diode anode, sinceit has little effect on the electron stream. It is particularly usefulthis way when the grid 5 is tied to the filament, even though at theexpense of a certain amount of rectification efficiency.

Of course, the tube 3 is not limited in its use to a superheteroclynereceiver, since it may be employed with equal efiiciency in a receiverof the tuned radio frequency amplifier type. Furthermore, while I haveindicated and described several systems for carrying my invention intoeffect, it will be apparent to one skilled in the art that my inventionis by no means limited to the particular organizations shown anddescribed, but that many modifications may be made without departingfrom the scope of my invention as set forth in the appended claims.

What I claim is:-

1. In combination with a radio frequency amplifier, a multifunction tubeincluding a cathode, two anodes and at least two grids, an input circuitcoupled to said amplifier and connecting one of said anodes to saidcathode, said input circuit including an impedance and coacting withsaid one anode and cathode to provide a diode rectifier, means forconnecting one of said grids to a point on said impedance, means forconnecting the other anode to said cathode through a path which includesa source of positive anode potential, said point supplying the audiofrequency component of the potential developed across said impedance tosaid one grid, an automatic gain control connection between saidimpedance and the amplifier, said other grid being disposed between saiddiode anode and the cathode and being maintained at substantiallycathode potential whereby the development of a bias voltage across saidimpedance is substantially prevented.

2. In an arrangement as defined in claim l, said diode anode beingdisposed in the electron stream from said cathode to said two grids andremaining anode, said diode anode being so constructed and arranged asto draw only a portion of said electron stream.

3. In an arrangement as defined in claim l, at least two additionalgrids disposed within said tube, the grid having the connection to saidimpedance being disposed between said two additional grids, and meansfor maintaining said two additional grids at a positive potential withrespect to the cathode.

4. In a radio receiver, a multiple function tube including a filament, aplate, and five grids disposed between the filament and plate, one ofsaid grids being constructed and arranged to draw only a portion of theelectron stream from said filament, a signal input circuit including aresistor connected between said one grid and the filament and providinga diode detector circuit, a second one of said grids being disposedbetween said first grid and said filament and being connected to saidlament whereby itis at filament potential, a third one of said gridsbeing connected to a point on said resistor whereby the audio componentof rectified signals is fed to said third grid, and the said third gridbeing disposed between the remaining two grids, means for maintainingthe remaining two grids and said plate at a positive potential withrespect to the filament whereby the audio component is amplified in saidplate circuit.

5. In a radio receiver as defined in claim 4, means for connecting saidfilament to a 2 volt heating source, and a direct current automaticvolume control connection connected to the negative side of saidresistor.

6. In a receiving system, a tube provided with at least a cathode, apositive plate, and an auxiliary electrode disposed in the electronstream between the cathode and plate, the electrode being constructedand arranged to draw only a portion of the stream from the cathode, asignal input circuit including an impedance connected between saidcathode and auxiliary electrode and providing a diode rectifier circuit,an automatic gain control connection connected to a point on msaidimpedance, a cold electrode disposed in said stream betweenl saidcathode and auxiliary electrode, and said co-ld electrode beingmaintained substantially at cathodepotential whereby said point isprevented from assuming a substantial negative potential with respect tothe cathode when no signals are impressed on said input circuit.

7. In combination, an electron discharge tube provided with a cathode,an anode and a plurality of electrodes interposed between the cathodeand anode, a diode rectifier circuit including an impedance connectedbetween the cathode and one of the interposed electrodes, second fromthe cathode, an automatic gain control connection to f a point on saidimpedance, and a direct electrical connection between the cathode andthe electrode next adjacent thereto.

8. In combination, an electron discharge tube provided with a cathode,an anode and a plurality of electrodes interposed between the cathodeand anode, a diode rectifier circuit including an impedance connectedbetween the cathode and one of the interposed electrodes, second fromthe cathode, a source of signal frequency coupled to said rectifiercircuit, a path connecting a point on said impedance and another of saidinterposed electrodes whereby the audio component of rectified signalsis impressed thereon, an automatic gain control connection to a point onsaid impedance, a direct electrical connection between the cathode andthe electrode next adjacent thereto, and an output circuit connectedbetween the anode and cathode.

9. In combination, an electron discharge tube provided with a cathode,an anode and a plurality of electrodes interposed between the cathodeand anode, a signal input circuit connected between.

one of said interposed electrodes and the cathode, an output circuitconnected between cathode and anode, a diode rectifier circuit coupledto said output circuit including an impedance and connected between thecathode and one of the interposed electrodes, second from the cathode, apath connected to a point on said impedance for deriving an audiofrequency component from the rectified signals, an automatic gaincontrol connection to a point on said impedance, and a direct electricalconnection between the cathode and the electrode next adjacent thereto.

DON G. BURNSIDE.

